Radio navigation systems, for example the LORAN system (Long-range navigation), are known in the art from, for example, seafaring. In these systems, pulses or signals are transmitted at fixed points in time from a number of fixed stations. In a receiver, for example a ship, the position of the ship is determined from the differences in the signal transit times of the signals received.
However, the accuracy of the positional determination lies in a range of inaccuracy of several 100 meters. A more accurate position-determining system is the GPS (Global Positioning System), in which time information of a highly accurate clock is additionally transmitted by satellites.
The Global Positioning Systems cannot be used to locate the position of an object, for example, inside a building or a motor vehicle, since the signals of the satellites are blocked even by relatively small items.
To determine the position of an object inside a building, a system similar to the LORAN system is disclosed in Matthew S. Reynolds: “A Phase Measurement Radio Positioning System for Indoor Use”, M.I.T., Feb. 3, 1999. In this method, the position in a building is determined with the aid of transit time measurements, similar to the LORAN system. The transmitters in this case transmit sinusoidal signals at low frequency. The position is determined by differences in transit times.
Each transmitting signal is necessary if positions are to be determined exactly using the known systems many transmitting stations. Only then can a spatial position be determined. For a more accurate positional determination, additional correction-signal transmitters are necessary, for example in the case of DGPS (Differential GPS).